The existing tricone rock bit usually includes a bit body with three head sections, a cone is rotatably mounted on bearing shaft inclined at lower ends of the head sections, the cone having steel cutting elements or cemented carbide inserts, and drilling fluid is pumped into a drill fluid course from a drill string, and then is discharged out of three nozzles. Each nozzle is mounted in a nozzle boss, and the nozzle bosses are disposed at rear sides of the head sections. The drilling fluid impacts the well bottom and then returns back up from both sides of the nozzle boss. The bit contacts the borehole wall at three points on a heel row of cutting elements of the cones, and the point of contact is on a leading side of each cone. When horizontal wells and hard formation wells are drilled, the roller cone bit has the following problems: quick lateral movement and strong impact result in deviation of the center of rotation of the bit from its geometric center and acceleration of wear and break of the cutting elements, and even lead to premature bearing failure; due to gravity, removal of drilling cuttings from the well bottom is poor, which also easily results in that the cone shell wears and cutting elements breakage or loss; the water jet orientation is unreasonable, and the cutting elements are not timely cooled accordingly, thereby accelerating the wear. Wear-resistant cutting elements are arranged above OD of the head sections (head OD) to resist lateral vibration, but they cannot adequately suppress severe lateral vibration as the cutting elements arrangement center on the OD of the head sections is usually on the axis of the head sections.
U.S. Pat. No. 6,227,314 (entitled “INCLINED LEG EARTH-BORING BIT”) changes the conventional rear nozzle boss into a front nozzle boss, the upper portion of the head OD is offset circumferentially a distance relative to the lower portion, a gage point is formed on the upper portion of the head OD, the nozzle boss and the lower portion of the leg form a mud up-return channel, but the channel changes its direction on the upper portion of the leg, not helpful for smooth up-return of the mud.
U.S. Pat. No. 6,688,410 (entitled “Hydro-lifter rock bit with PDC inserts”) cancels the cone gage point, but disposes the gage point on the upper portion of the head OD, the geometric centerline on the upper portion of the head OD is parallel to the centerline of the bit, and the geometric centerline on the lower portion is at an angle to the centerline of the bit. In this patent, the borehole diameter is formed by cutting action of the head OD, which can decrease drilling efficiency of the bit.